The present invention is directed to a control system and method for internal combustion engines, and more particularly, concerns a powertrain output monitor for electronic throttle control-equipped vehicles.
Electronic airflow control systems, such as variable cam timing systems and electronic throttle control systems, replace traditional mechanical throttle cable systems with an xe2x80x9celectronic linkagexe2x80x9d provided by sensors and actuators in communication with an electronic controller. This increases the control authority of the electronic controller and allows the airflow and/or fuel flow to be controlled independently of the accelerator pedal position.
To control the actual output engine brake torque to achieve the driver-demanded wheel torque, it is desirable to calculate a corresponding desired engine torque. The desired engine torque is then mapped into a desired airflow and fuel flow. The desired airflow can be affected by the air-fuel ratio, phase angle of a variable cam timing (VCT) actuator, and/or percent of exhaust gas recirculation (EGR). Degradation or drifting on any air sensing or control device such as the throttle actuator, throttle position sensor, mass airflow (MAF) sensor, intake manifold pressure (MAP) sensor, VCT sensor, EGR flow sensor, or universal exhaust gas oxygen (UEGO) sensor.
In general, the task of any powertrain monitoring system is to determine if the actual wheel torque is different than that demanded by the driver and may reduce the difference with the electronic throttle, fuel injectors, or spark timing.
With conventional approaches to mapping the desired engine torque to a desired airflow, sensitivity to different components depends largely upon the method of mapping the driver""s request into the actual mass airflow through the throttle.
Accordingly, there is a need for an improved powertrain output monitor having a reduced sensor set.
It is an object of the present invention to provide a system and method for engine torque control in an engine having electronically controlled airflow and/or fuel flow.
Another object of the present invention is to provide a system and method for engine torque control having improved accuracy of generating driver demanded torque. Another object is to reduce the sensor set relied upon by the engine monitor system.
The foregoing and other objects, advantages, and features of the present invention are provided by a method of controlling the power output of an engine having at least one fuel injector responsive to a commanded fuel signal. The method includes the steps of determining a desired engine power, and determining a first fuel flow value as a function of the desired engine power and engine speed. This first fuel flow value is then compared to the desired fuel flow signal generated by the air-fuel ratio controller. The commanded fuel signal is then limited by the lesser of the desired fuel flow and first fuel flow value. In one aspect of the invention, the desired engine power is calculated by determining a first power value as a function of engine speed and a desired engine torque, and determining a second power value as a function of turbine speed, driveline efficiency and a desired wheel power. The desired engine power is then selected as the lesser of the first and second power values. In another aspect of the invention, the first fuel flow value is modulated by static and dynamic tolerance margins to prevent fuel limiting during normal engine operation.
The present invention provides a number of other advantages over prior art powertrain output monitoring strategies. The system is inherently simple because of its reduced sensor set which improves robustness and has advantages for implementation.